Counterfeit of paper currency damages greatly not only the economy of a Nation, adopting that particular paper currency, but also the Countries with which the Nation has import-export trade.
The development of the EEC and fall of the barriers within Eastern Europe have increased the counterfeit business.
The U.S. Dollar is the most counterfeit currency, because of its wide distribution.
The possibility of using chemical solutions for detecting counterfeit paper currency must be conducted without leaving any stain on the countersigning banknote, according to the laws of the Countries which forbid marking on any kind of paper currency.
Presently, there are available on the market some devices, using chemical solutions, for detecting counterfeit paper currency.
In U.S. Pat. No. 5,603,163 a chemical solution is described, for detecting counterfeit paper currency, that includes a high concentration of iodine and iodides in an alkaline aqueous-alcoholic solutions and in the presence of elevated hydrogen peroxide concentrations.
When said solution is used to draw a line on a banknote, this drawn line become brown and permanently persists on all countersigned banknotes, even if they are genuine: that is forbidden by all National laws.
Moreover, this cited patent describes the use of toxic or cancerogenic solvents in the chemical solution, such as carbon disulfide, carbon tetrachloride, and chloroform.
Document WO-A-84/03295 discloses an ink composition for use in ink jet printing comprising an aqueous solution of a water soluble dye, a starch staining combination and a viscosity enhancer.
The most important features of this ink are:
increased optical density of a printed dot, achieved by the sum of tinctorial effects of dye on cellulose and KI+I.sub.2 starch sizing reaction; PA1 omission of bacteriocide, due to relatively high iodine concentration; PA1 increased water and light permanency.
This ink stains or marks a starch content paper such as xerographic papers, bond papers, cotton filled papers, all of which have a high starch content.
Ink solution always includes a commercial liquid dye together with the KI.sub.3 +I.sub.2 radical ion combination that reacts with the starch in the paper to produce an organic complex that has a very deep blue colour.
This ink solution is used to provide a significant increase in the optical density of every printing made with the ink itself in comparison with the standard ink.
When said ink solution is used to draw a line on a banknote this drawn line will lie permanently on the countersigned banknotes, due to the high concentration of KI.sub.3 and the low volatility of said ink solution.
The described solution and other known solutions have not resolved in a fully effective way the problems connected with the safe detection of counterfeit paper currencies.